Focusing on the problem of lack of independent cache module of original iSCSI target controller, we introduce a fusion cache mechanism based on flash memory called FusionCache into the iSCSI target software to further improve the overall performance of the storage area network. FusionCache uses flash memory and DRAM to form a unified fusion cache architecture. The flash memory acts as DRAM's expansion space, and DRAM is divided into cache block metadata area (metadata cache) and front-end buffer area (front cache). The metadata cache manages cache block metadata based on radix tree in order to accelerate the cache block searching; the front cache tallies and predicts the access popularity of the cache block based on regressing fitting model, and absorbs the impact of massive writes on flash memory to ensure that only the hot data is allowed to enter the flash memory. FusionCache uses the improved LRU algorithm to do cache replacement. Besides, it takes iSCSI session's state into account during write-back. The experimental results show that: FusionCache is able to reduce access to backend disk devices, and improve I/O response speed. FusionCache reduces I/O access latency by 33% and 60%, and improves throughput by 25% and 54%, compared to cache mechanism with only DRAM and original iSCSI target, respectively. Compared with Flashcache proposed by Facebook, FusionCache improves throughput by 18% and reduces latency by 27%. FusionCache also has a good read cache hit rate. Besides, FusionCache reduces write amount of flash memory, thus extends its life. FusionCache provides good efficiency of network storage and reduces cost.